Composition, temperature and humidity dependence of ionic conductivity in polyethylene oxide (PEO):NH4ClO4 polymer electrolyte composite obtained by the dispersal of Al2O3 is reported. The dispersal of Al2O3 introduces significant changes in the conductivity vs. composition isotherm. The conductivity of the composite peaks at two concentrations of Al2O3 is similar to 2 x 10(-5) S cm(-1). For studying ion dynamics, motional narrowing of H-1 NMR line with temperature is also reported. In PEO:NH4ClO4 (without dispersed Al2O3), two H-1 frequency-shifted NMR lines are seen (one of these have been assigned to the H-1 belonging to -CH2-CH2- chain of the polymer and the other to NH4 (+) complexed with the chain). For the (PEO:NH4ClO4) + Al2O3 composites, however, one additional narrow peak is also seen at temperatures higher than 40 A degrees C. This has been interpreted in terms of some hopping H+ ions getting loosely bonded to Al2O3, forming Al(OH)(3), which possibly releases an additional mobile protonic species (OH-).